Some would say that the process of separation through the use of high-grade silica and other chromatographic materials will eventually result to separation of impurities so it's okay to use technical grade solvents. However, do some of you people have other thoughts on this? Is efficiency and quality of separation compromised with lower grade solvents?
Thanks for answering.
The answer is : it depends. It depends on the nature of the solvent impurities, your compound retention, and your chromatography.
If you have sharp peaks for the desired compound, the contamination from solvent impurities will be minimal to none, unless the impurities are focused and elute at the same time as your compound.
If your compound elutes as a wide peak, assuming the column doesn't hold up the impurities, you stand a greater chance of concentrating the impurities with your compound. Concentrating a couple of liters of solvent will often yield several milligrams of impurity. However, depending on the chromatography, the column will often trap non-volatile impurities.
If the impurity is something like trace amounts of cyclohexene in cyclohexane, you'll likely evaporate the impurity when you evaporate the solvent.
Can you tell us more about the chromatography? You may want to research "ghost peaks" as some of these arise from solvent impurities.
Jack Silver Thank you for your detailed response.
I'm planning to use silica gel 60 and/or Sephadex LH-20 as my stationary phases. My samples are alkaloids from a plant, some of them are known and some are not. Thinking about it, my end goal is not to fully isolate these compounds (but it would be great if I could!), that's why I was trying to reconsider the suggestion to use lower grade solvents that are more affordable...but I'm skeptic about this and wanted to know if it is an acceptable practice.
I am currently checking the impurities for each solvent that I will be using (water, MeOH, EtOAc, EtOH). For now, my mind tells me to buy the AR grade just to be sure. Still, it would be good if I could save some $$$ with technical grade solvents, especially that I will probably do multiple runs to get higher yields.
You mentioned that evaporation of the solvent/s from the collected fractions would likely remove the contaminants. I still have to look into the impurities and check if they're volatile. But this tip was really helpful. Thanks!
I have used hplc equipments for 20 years and never used hplc grade solvents. A gradient will help you move your peak of interest from impurities.
Joyce Gem Cañete It is an acceptable practice, so long as you understand its limitations. Evaporation will remove some of the contaminants, if they are volatile. Take a look at the specifications sheets for your solvents, there is usually a limit listed for non-volatile compounds. It is usually ppm, but remember that when several liters of solvent are evaporated, a few ppm means a few milligrams!
It is excellent to use if you have the money to buy in huge quantity
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